Circadian actions of orexins on the retinorecipient lateral geniculate complex in rat

• Published in: The Journal of physiology Vol. 599; no. 1; pp. 231 - 252
• Main Authors: Chrobok, Lukasz, Jeczmien‐Lazur, Jagoda Stanislawa, Pradel, Kamil, Klich, Jasmin Daniela, Bubka, Monika, Wojcik, Michal, Kepczynski, Mariusz, Lewandowski, Marian Henryk
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01-01-2021; John Wiley and Sons Inc
• Subjects: Animals; Arousal; circadian clock; Circadian Rhythm; Circadian rhythms; Geniculate Bodies; Hypothalamic Area, Lateral - metabolism; Hypothalamus (lateral); Information processing; Lateral geniculate nucleus; multi‐channel electrophysiology; Neuromodulation; neuronal tract tracing; Neurons; Neurons - metabolism; Neuroscience; optogenetics; Orexin receptors; Orexin Receptors - metabolism; Orexins; Orexins - metabolism; PAC1 protein; PAC1 receptor; Pituitary adenylate cyclase-activating polypeptide; Rats; Research Paper; retinorecipient; subcortical visual system; Visual system; neuronal tract tracing; optogenetics; subcortical visual system; orexins; circadian clock; lateral geniculate nucleus; multi-channel electrophysiology; PAC1 receptor; retinorecipient
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP280275

Key points
Rhythmic processes in living organisms are controlled by biological clocks. The orexinergic system of the lateral hypothalamus carries circadian information to provide arousal for the brain during the active phase.
Here, we show that orexins exert an excitatory action in three parts of the lateral geniculate nucleus (LGN), in particular upon directly retinorecipient neurons in the non‐image forming visual structures.
We provide evidence for the high nocturnal levels of orexins with stable circadian expression of predominant orexin receptor 2 in the LGN.
Our data additionally establish the convergence of orexinergic and pituitary adenylate cyclase (PAC)‐activating peptide/PAC1 receptor systems (used by melanopsin‐expressing retinal ganglion cells), which directly regulates responses to the retinal input.
These results help us better understand circadian orexinergic control over the non‐image forming subcortical visual system, forming the animal's preparedness for the behaviourally active night.
The orexinergic system of the lateral hypothalamus is tightly interlinked with the master circadian clock and displays daily variation in activity to provide arousal‐related excitation for the plethora of brain structures in a circadian manner. Here, using a combination of electrophysiological, optogenetic, histological, molecular and neuronal tracing methods, we explore a particular link between orexinergic and visual systems in rat. The results of the present study demonstrate that orexinergic fibre density at the area of subcortical visual system exerts a clear day to night variability, reaching a maximum at behaviourally active night. We also show pronounced electrophysiological activations of neurons in the lateral geniculate nucleus by orexin A through 24 h, via identified distinct orexin receptors, with the ventrolateral geniculate displaying a daily cycle of responsiveness. In addition, for the first time, we provide a direct evidence for orexins to act on retinorecipient neurons with a high convergence of orexinergic and putatively retinal pituitary adenylate cyclase (PAC)‐activating peptide/PAC1 receptor systems. Altogether, the present study ties orexins to non‐image forming visual structures with implications for circadian orexinergic modulation of neurons, which process information on ambient light levels.
Key points
Rhythmic processes in living organisms are controlled by biological clocks. The orexinergic system of the lateral hypothalamus carries circadian information to provide arousal for the brain during the active phase.
Here, we show that orexins exert an excitatory action in three parts of the lateral geniculate nucleus (LGN), in particular upon directly retinorecipient neurons in the non‐image forming visual structures.
We provide evidence for the high nocturnal levels of orexins with stable circadian expression of predominant orexin receptor 2 in the LGN.
Our data additionally establish the convergence of orexinergic and pituitary adenylate cyclase (PAC)‐activating peptide/PAC1 receptor systems (used by melanopsin‐expressing retinal ganglion cells), which directly regulates responses to the retinal input.
These results help us better understand circadian orexinergic control over the non‐image forming subcortical visual system, forming the animal's preparedness for the behaviourally active night.